DESCRIPTION: (Investigator's abstract): The application's broad, long-term objectives are to increase our understanding of the functional organization of the visual pathways. The aims of Experiment I and II are to study the retinal, cortical, and intrageniculate contributions to the orientation sensitivity of different types of LGNd relay cells in cats and monkeys, respectively. The aim of Experiment III is to alter the distribution of retinal ganglion cell dendritic field orientations in newborn cats and then, in the adult, to study the orientation sensitivity and morphologies of the altered retinal ganglion cells and the LGNd relay cells and cortical cells which subserve them. The aim of Experiment IV is to study the proportion and distribution of orientation sensitive cells in layer 4c beta of monkey striate cortex. The relationship between the orientation biases of layer 4c beta cells and the orientation preferences of the simple and complex cells in the layers above and below them will also be studied. The experiments will be carried out using standard surgical procedures and computer controlled, quantitative procedures for studying the visually evoked responses of single cells in the visual pathways. Cortical inactivation and the simultaneous recording of action potentials and S potentials will be used to infer the relative contributions of cortical afferents, retinal afferents and intrageniculate mechanisms to the responses of LGNd relay cells. HRP histochemistry, DiI fluorescence labeling, and computerized morphometric analyses will be used to study neuronal morphology. Statistical tests designed specifically to analyze our data will be employed. The proposed studies should 1) increase our understanding of the functional organization of the LGNd, 2) elucidate the function of the corticogeniculate projection, 3) clarify the relationship between cortical and subcortical orientation sensitivity, and 4) provide information which will help us to better understand how form and color are encoded in the M and P cell pathways in primates.